Antenna and matching circuit



1952 N. E. LINDENBLAD ANTENNA AND MATCHING CIRCUIT Filed Sept. 12, -1946mad 71; BY

COIVOUCT/I E JHEET GP.

l GROUND FLA/V5 Patented Oct. 21, 1952- ANTENNAIYAND MATCHING CIRCUITNils E. Lindenblad, Port Jefferson, N. Y., assignor to Radio Corporationof America, a corporation of Delaware Application September 12, 1946,Serial No. 696,556

Still a further object of the present invention is the provision of asimple means for matching'a transmission line to a broadband antenna.

Another object of the present invention is the provision of a matchingsystem which will enablethe matching of a transmission" line to anantenna over a wide range of conditions by a simple adjustment of theproportions of parts of the matching circuit.

The foregoing objects and others which may appear from the followingdetaileddescri'ption are attained by providing anantenna in'the form ofa hollow conductive member having transverse dimensions which are largein terms of the operating wavelength. Ordinarily the radiator will"beso'po'sitioned as to extend perpendicularly'away from a conductivesheet. A coaxial transmission line is arranged to pierce the groundsheet and extend into the hollow interior of the radiator. The innerconductor of the transmission line'is so arranged to extend further intothe hollow interior of the radiator than the outer shell.-

By proportioning the relative extensions 'of the outer shell and innerconductor into hollow interior'of the radiator, the input impedance ofthe radiator may be easily matched to any convenient transmission lineimpedance. The pro-' trusion of the inner conductor beyond the outerconductor of the transmission line is smaller the higher the matching.impedance required. The outer conductor of the transmission line is atthe same time longer.

Thepresentv invention will be more fully understood by reference to thefollowing detailed de-; scription which is accompanied by a drawing inwhich; v

- Figure 1 illustrates in transverse cross section anxelementary type ofvertical radiator known in; the art'which isutilized as a basis for thematching circuit ofthe present invention, while .Figure 2 illustrates intransverse section an embodiment of the present invention, and

-gures 3 and 4 illustrate modification'sthereof; A

Referring'now to Figure lth 'ereis shown 'a" conductive sheet GP whichmay-under some 13 Claims. (Cl. 250-33) 2 circumstances be the outerconductive skin of an airplane or it may be a flat metal roof on the topof a tall building. Beneath ground plane GP is a concentric transmissionline having an outer shell i0 and an iner conductor I 2. Thetransmission line extends through the ground sheet GP at right angles tothe plane of the sheet to form'a quarter wave antena. The outer shellI!) of the transmission line may extend approximately one third of thedistance up from the ground sheet GP as a sleeve 28 while. the innerconductor extends a further distance as a radiator 22. Theoverall'length of the radiat-' ing fportion of the antenna 'isapproximately one quarter wavelength at the operating frequency. I InFigure 2 the ground sheet and transmission line arrangement is the same,as described with reference to Figure 1. However, in this modificationthe radiator itself is in the form of a hollow conductive member [9closed at the top and connectedto groundplane GP by connection It. atransverse dimensionwhich' is fairly large in terms of the operatingwavelength; for example, somewhere between one eighth and threesixteenths of the operating wavelength. radiator I 9 thus possessesbroad band characteristics. proximately a quarter wavelength. Thetransmission line is coupled to the interior of radiator Ill by theextension of sleeve 20 and extending conductor 22 within the hollowinterior of radiator l9. Sleeve 28 is provided with an upper slidablesleeve 2| and member 22 is provided with a slidable outer sleeve 23whereby the relative extensions of these members within the radiator I!)may readily be adjusted. By adjusting these extensions the 'efiectiveimpedance of theantenna, as seen from the transmission line TL, may beadjusted to perfectly match 'the radiator l9 to the transmission line.The

30 around its lower edge. The flange 39 is electrically and mechanicallyconnected to the. ground plane GP. The transmission line arrangement inFigure 3 is the same as in Figure 1.

.As so 'far described the arrangement of Fig.3 permits the coupling ofthe transmission "line TL to the interior of radiatormember 2.! but inthe absence of any communication between the interior and exterior ofmember 29110 radiation would be possible. Therefore, I have provided a tseries of apertures or'circumferentially extending It is preferred thatmember [9 have The overall length of radiator I9 is -ap'-' slots 3|around the base of the radiator member 29 by means of which the interiorthereof may be coupled to the exterior. The outside dimensions ofradiator 29 and the extent of the coupling provided by slots 3| efiectsto some extent the required extension of sleeve 20 and inner conductor22 into the interior of radiator 29 to provide a match to any giventransmission line. However, where a 50 ohm transmission line is used theouter sleeve 20 of the transmission line may extend over two thirds ofthe length of the inner conductor within radiator 29 and above groundplane GP while the inner conductor may extend nearly to the top ofmember 29. It will thus be seen that I have provided a radiator whichissturdily constructed while still having a broad band characteristic.The excitation system permits a wide range of impedance transformationand reactance balancing.

Figure 4 shows a further modification of Figure 2. Here radiator 39 issimilar to radiator l9, except that it is approximately a half wave inlength. The transmission line arrangement within the radiator is thesame as in previous figures except that due to the greater length ofradiator 39, it terminates at somewhere near the center thereof. Iheinterior of radiator 39 is coupled to the exterior by apertures 4| atthe midsection.

While I have illustrated a particular embodiment of the presentinvention, it should be clearly understood that it is not limitedthereto since many modifications may be made in the several elementsemployed and in their arrangement without departing from the spirit andscope of the invention.

What is claimed is:

1. A broad band antenna system including a radiation transferringelement comprising an elongated hollow conductive member closed at onevend and arranged substantially normal to one side of a conductive groundplane system, and means to transferenergy from said hollo-w member to autilization device, said means comprising a length of coaxialtransmission line of given characteristic impedance having sleeve andinner conductors extending into said hollow member, said sleeveconductor being connected to said ground plane system and said innerconductor extending into said hollow member to a greater distance thansaid sleeve conductor, the distances of the extension of said conductorsinto said hollow member having values at which the impedance of saidhollow member at the operating wavelength is substantially matched tosaid given characteristic impedance plane system, said hollow conductivemember having longitudinal and transverse dimensions large interms ofthe operating wavelength and having, the longitudinaldimensionsextending in a direction substantially normal to said ground planesystem, and means to transfer energy from said hollow member to autilization device, said means comprising a length of coaxial transmis-'sion line of given characteristic impedance having sleeve and innerconductors extending into said hollow member. said sleeve conductor onlybeing connected to said ground plane system and said inner conductorextending into said hollow member to a greater distance than said sleeveconductor, the sole coupling of said inner conductor to said hollowmember being by radiation of energy therebetween, the distances of theextension of said conductors into said hollow member having values atwhich the impedance of said hollow member at the operating wavelength issubstantially matched to said given characteristic impedance of saidcoaxial transmission line section.

3. An antenna system including a radiation transferring elementcomprising an elongated hollow conductivev member closed at one end andarranged to one side of a conductive ground plane system, said hollowconductive member having longitudinal dimensions of at least a quarterof the operating wavelength extending in a direction substantiallynormal to said ground plane system transverse dimensions of at least aneighth of the operating wavelength, and means to transfer energy fromsaid hollow member to a utilization device, said means comprising alength of coaxial transmission line of given characteristic impedancehaving sleeve and inner conductors extending into said hollow member,said sleeve conductor only being connected to said ground plane systemand said inner conductor extending into said hollow member to a greaterdistance than said sleeve conductor, the distances of the extension ofsaid conductors into said hollow member having values at which theimpedance of said hollow member at the operating wavelength issubstantially matched to said given characteristic impedance of saidcoaxial transmission line section, said inner conductor being free ofany direct current connection to said hollow member.

4. A broad band antenna system including a radiation transferringelement comprising an elongated hollow conductive member closed atoneend and arranged substantially normal to one side of a conductive groundplane system, the end of said hollow member remote from said one endbeing connected to said conductive ground plane system, there beingapertures therein interconnecting the interior of said hollow memberwith ambient space, and means to transfer energy from said hollow memberto a utilization device, said means comprising a length of coaxialtransmission line of given characteristic impedance having sleeve andinner conductors extending into said-hollow member, said sleeveconductor only being connected to said ground plane system and said.inner conductor extending into said hollow member to a greater distancethan said sleeve conductor, the distances of the extension of said iconductors into said hollow member having values at which the impedancof said hollow member at the operatin wavelength is substantiallymatched to said given characteristic impedance of said coaxialtransmission line section said inner conductor being free of any directconnection to said hollow member.

5. An antenna system for operation in conjunctionwith a-conductiveground sheet, including an elongated conductive dome having a flangethan said sleeve conductor and being free of any direct currentconnection to said conductive dome.

6. An antenna system for operation in conjunction with a conductiveground plane system, including a hollow, substantially closed, elongatedconductive member having a plurality of circumferentially arranged slotstherein, a section of coaxial transmission line of given characteristicimpedance and having sleeve and inner conductors extending into saidhollow conductive member with the inner conductor extending therein agreater distance than the sleeve conductor, the sleeve conductor beingconnected to said conductive member at the point of entry therein, andsaid member being connected to said conductive ground plane system, thedegree of extension of said conductors into said hollow member having avalue at which the operating impedance of said hollow member issubstantially matched to the characteristic impedance of said coaxialtransmission line, the sole coupling between said inner conductor andsaid hollow member being by radiation therebetween.

'7. A broad band antenna system for operation in conjunction with aconductive ground sheet, including an elongated conductive dome having aflange at the base thereof and a plurality of slots therein near thebase, a length of coaxial transmission line having sleeve and innerconductors extending into said dome, said sleeve conductor beingelectrically connected to said flange, said inner conductor extendinginto said dome to a greater distance than said sleeve conductor, thesole connection between said conductors and said dome being a connectionof said sheath conductor to said ground slot substantially at saidflange.

8. A broad band antenna system for operation in conjunction with aconductive ground plane system, including a hollow substantially closed,elongated. conductive member having a plurality of circumferentiallyarranged slots therein and being connected to said conductive groundplane system, a section of coaxial transmission line having sleeve andinner conductors extending through said ground sheet and into saidhollow conductive member with the inner conductor extending therein agreater distance than the sleeve conductor, the sleeve conductor beingconnected to said conductive member at the point of entry therein toform the sole direct connection between said conductors and saidconductive member.

9. A broad band antenna system for operation in coniunction with aconductive ground sheet, including an elongated hollow conductive memberclosed at one end and arranged substantially normal to the plane of saidground sheet, there being at least one aperture near the lower end ofsaid hollow member and said ground sheet, a section of coaxialtransmission line havin sleeve and inner conductors extending throughsaid ground sheet into said hollow conductive member, said innerconductor extending into said hollow conductive member to a greaterdistance than said sleeve conductor, said inner conductor being free ofconnection with said conductive member, and the end of said conductivemember adjacent said round sheet and said sleeve conductor beingconnected to said ground sheet.

10. An antenna system for operation in conjunction with a conductiveground sheet, including an elongated hollow conductive member closed atone end and. arranged substantially normal to the plane of said groundsheet, and a section of coaxial transmission line having sleeve andinner conductors extending into said hollow member, said sleeveconductor being connected to said ground sheet, said inner conductorextending into said hollow conductive member to a greater distance thansaid sleeve conductor, and said inner conductor being free of connectionwith said conductive member.

11. An antenna system for operation in conjunction with a conductiveground sheet, includ ing an elongated hollow conductive member ,closedat one end and arranged substantially normal to the plane of said groundsheet, a section of coaxial transmission line having sleeve and innerconductors extending into said hollow conductive member, said innerconductor extending into said hollow conductive member to a greaterdistance than said sleeve conductor, said inner conductor being free ofconnection with said conductive member, said conductive member havingapertures therein, and the end of said conductive member adjacent saidground sheet and said sleeve conductor being connected to said groundsheet.

12. An antenna system for operation in conjunction with a conductiveground sheet, including an elongated hollow conductive member closed atone end and having the other end connected to said ground sheet, asection of coaxial transmission line having sleeve and inner conductorsextending into said hollow conductive member, said inner conductorextending into said hollow conductive member to a greater distance thansaid sleeve conductor, said inner conductor being free of connectionwith said conductive member, said conductive member having aperturestherein near the point of connection to said ground sheet and saidsleeve conductor being connected to said ground sheet.

13. An antenna system for operation in conjunction with a conductiveground sheet, including an elongated hollow conductive member closed atboth ends and arranged substantially normal to the plane of said groundsheet, a section of coaxial transmission line having sleeve and innerconductors extending into said hollow conductive member, said innerconductor extending into said hollow conductive member to a greaterdistance than said sleeve conductor, said inner conductor being free ofconnection with said conductive member, said conductive member havingapertures therein substantially midway of the ends thereof, and the endof said conduc' tive member adiacent said ground sheet being connectedto said ground sheet by said sleeve conductor.

N'ILS E. LINDENBLAD.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number

